Chemical nickel plating

ABSTRACT

A process for the chemical nickel plating of catalytic materials wherein the plating bath utilized in the process consists of an aqueous solution containing nickel cations and a low concentration of hypophosphite ion together with a series of additives which include fluorides, succinates, a lead salt, lactic acid, boric acid, and a complexing and wetting agent such as an alkylphenoxy(ethyleneoxy)ethanol and wherein the bath is adjusted to pH 5-5.5 with ammonium hydroxide and is operated at a temperature of 75*-85*C. The invention also includes a method for preventing the deposit of nickel on heating and containing equipment which consists of connecting the equipment anodically to a small direct current.

United States Patent El-Mohamad Sept. 2, 1975 CHEMICAL NICKEL PLATING OTHER PUBLICATIONS [751 Inventor: Zlad Huntsfille IBM Tech. DiSCl. 131111., v61. 9, N0. 11, April 1967.

Kirk-Othmer, Encyclopedia Of Chem. Tech., 2nd Ed., [73] Assignee: GTE Automatic Electric 1969 pp. 533-536.

Laboratories Incorporated, Northlake, Ill. Primary ExaminerRalph S. Kendall [22] Filed: Jan. 15, 1973 l N 323 566 [57] ABSTRACT [2]] App O" A process for the chemical nickel plating of catalytic materials wherein the plating bath utilized in the process consists of an aqueous solution containing nickel 427/438 cations and a low concentration of hypophosphite ion [51] Int. Cl.2 together a eries of additives which include fluo- Field Of Search 117/130 E, 47 rides, succinates, a lead salt, lactic acid, boric acid,

1 18/620, 204/147 and a complexing and wetting agent such as an alkylphenoxy(ethyleneoxy)ethanol and wherein the bath is References Cited adjusted to pH 5-5.5 with ammonium hydroxide and UNITED STATES PATENTS is operated at a temperature of 7585C. The inven- 2,694,019 11 1954 Gutzeit 117 130 E also includes a method for Preventing the delmit 2,774,688 12/1956 Girard 117 130 E of nickel on heating and Containing equipment which 2,872,354 2/1959 Lee 117/130 E consists of connecting the equipment anodically to 21 2,893,929 7/1959 Schnable 204/32 S X small direct current.

3,485,725 l2/l969 Koretzky 117/130 E X 3,667,972 6/1972 Coll-Palagos 117 130 E x 9 Clams, N0 Drawlngs CHEMICAL NICKEL PLATING BACKGROUND OF THE INVENTION Chemical nickel plating of catalytic materials may be accomplished by treating such materials with a buffered aqueous solution containing a nickel salt and hypophosphite ion. This plating procedure is temperature sensitive and must normally be conducted just below the boiling point of the bath (90-l00C.), in order to achieve a high rate of nickel deposition. These high temperatures have a detrimental effect on the bath stability and result in wasted deposition of nickel on equipment used for heating and holding the solution.

Nickel is deposited on the catalytic surface as a result of reduction of nickel cations by the hypophosphite reducing agent. This reduction results in the formation of orthophosphite ions as a by-product, which by-product eventually precipitates as the nickel salt as the plating reaction proceeds. The precipitate serves to accelerate decomposition of the plating bath by providing additional surfaces for the deposition of nickel. The precipitate is also objectionable in causing a rough and unsatisfactory nickel deposit on the catalytic surface. High hypophosphite ion concentrations, utilized in previous high speed baths, are responsible for an increased tendency toward formation of a nickel orthophosphite precipitate and also result in an increased consumption of reducing agent.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an improved chemical process of plating with nickel which can be utilized at the convenient and relatively low temperature of 7585C. without the sacrifice of a rapid rate of nickel deposition.

Another object of the invention is to provide an improved process of the character described which employs a bath of the nickel cation-hypophosphite ion type which utilizes a low concentration of hypophosphite reducing agent.

Another object of the invention is to provide an improved plating bath of the type described which contains a complexing and wetting agent as an additive.

A further object of the invention is to provide an improved plating bath of the type described which contains a fluoride exaltant, succinates and lactates as exaltants, chelating agents and buffers, together with boric acid and ammonium hydroxide as buffers.

Still another objective of the invention is to provide an improved process of the type described in which nickel is prevented from depositing on heating and containing equipment by application of a small direct current to the bath in such a way that the heating and containing equipment are connected anodically. Other objects will appear hereinafter.

BRIEF SUMMARY OF THE INVENTION The invention consists of the discovery ofa new process for the chemical nickel plating of catalytic materials. The plating bath utilized in this process consists of an aqueous solution Containing nickel cations and a low concentration of hypophosphite ion together with a series of additives which include exaltants, chelating agents and buffers such as fluorides, succinates, lead salts, lactic acid, boric acid, and a complexing and wetting agent such as an alkylphenoxy(ethyleneoxy)ethanol. The bath is preferably adjusted to pH 55.5

(e.g. with ammonium hydroxide) and is capable of being operated at a temperature of 85C.

The invention also includes a method for preventing the deposit of nickel on heating and containing equipment which consists of connecting the equipment anodically to a small direct current.

DETAILED DESCRIPTION OF THE INVENTION Utilization of a relatively low bath temperature of 7585C. affords an improved bath stability which can be further improved by use of a low concentration of hypophosphite ion. This is accomplished, without sacrifice of a high rate of nickel deposition, by the use of fluoride ion as an exaltant together with succinates and lactates as exaltants, chelating agents, and buffers. The bath is preferentially utilized at a pH of 5-5.5 which can be controlled by the use of materials such as boric acid and ammonium hydroxide. The composition of the bath is such that a nickel coating, containing 4-8% phosphorus, is deposited on the catalytic surface at a rate of 20-28 microns per hour for a new bath and l8-23 microns per hour for a maintained bath. The optimum load (parts to be plated) is within the range of -100 square inches of surface area per gallon of solution.

The high surface tension of the plating bath can result in nonuniform deposition of nickel and excessive pitting of the deposit. Addition of a complexing and wetting agent corrects this difficulty and results in the formation of a uniform, nonporous, nonpitted and bright nickel deposit. Alkylphenoxypoly(ethyleneoxy)ethanols, which have the following general structure, have been found to be particularly suitable:

where R represents one or more alkyl substitutents having from 5-18 carbon atoms and n is a number from 6 to 20 with an optimal value of 19. The complexing and wetting agent reduces the surface tension of the plating bath and permits a free evolution of hydrogen gas during the catalytic reduction process. The alkylphenoxypoly(ethyleneoxy)ethanols are particularly satisfactory in view of their ability to withstand high temperatures and their stability toward the reducing and acidic nature of the bath.

In order to prevent wasted nickel from depositing on heating and containing equipment, a small direct current of 0.06-0.09 amp/cm may be applied with the equipment connected anodically in order to maintain constant passivation of the equipment.

The best mode contemplated for the practice of this invention is illustrated by the following examples.

EXAMPLE I An aqueous plating bath possessing the following composition was utilized:

Nickel sulfate 37 g/l Sodium hypophosphite 20 g/] Sodium succinatc 21 g/l Sodium fluoride 5 g/l Boric acid l2 g/l -Continued Lactic acid 21 g/l Alkylphenoxypoly(ethyleneoxy)- ethanol ().25 ml/l Lead sulfate I ppm The pH was adjusted to a value of 5-5.5 with ammo nium hydroxide and plating was conducted at a temperature of 82C. This plating bath was utilized without application of an electric current and contains lead sulfate as an anti-catalyst retarder to maintain the rate of nickel deposition within optimum limits. The nickel deposit was bright and was applied at a rate of 20-28 microns/hour.

EXAMPLE [I An aqueous plating bath possessing the following composition was utilized:

Nickel sulfate 39 g/l Sodium hypophosphite l8 g/l Sodium succinate 18.5 g/l Sodium fluoride 5.6 g/l Boric acid 12 g/l Lactic acid 21 g/l Alkylphcnoxypoly(ethyeneoxy)- ethanol 0.25 ml/l The pH was adjusted to a value of 55.5 with ammonium hydroxide and plating was conducted at a temperature of 77-85C. This bath was operated with the application of a 0.06-0.09 amp/cm direct current with the heating and containing equipment connected anodically. The nickel deposit was bright and was applied at a rate of 20-28 microns/hour.

The invention is hereby claimed as follows:

1. The process of chemically plating a catalytic surface with nickel by treating the surface with an aqueous bath consisting essentially of a nickel salt, a hypophosphite, a complexing and wetting agent, a fluoride exaltant, a lead salt, succinates and lactates as exaltants, chelating agents and buffers, together with boric acid and ammonium hydroxide as buffers wherein the concentration of hypophosphite is approximately 0.l to 0.3 mole/liter and the nickel ion concentration is approximately 0.2 to 0.3 mole/liter.

2. The process set forth in claim 1, wherein the complexing and wetting agent is an alkylphenoxypoly(ethyleneoxy)ethanol having the following structure:

where R represents one or more alkyl substituents having from 5 to 18 carbon atoms and n is a number from 6 to 20 with an optimal value of 19.

3. The process set forth in claim 1, wherein the initial pH of the bath is in the approximate range of 5.0 to 5.5.

4. The process set forth in claim 1, wherein the plating bath is utilized at a temperature in the approximate range of 85C.

5. The process of chemically plating a catalytic surface with nickel by treating the surface with an aqueous bath consisting essentially of a nickel salt, a hypophosphite, a complexing and wetting agent, a fluoride exaltant, succinates and lactates as exaltants, chelating agents and buffers, together with boric acid and ammonium hydroxide as buffers, wherein the concentration of hypophosphite is in the approximate range of 0.1 to 0.3 mole/liter and the nickel ion concentration is in the approximate range of 0.2 to 0.3 mole/liter, and wherein a small direct current is applied to the bath with the plating equipment connected anodically.

6. The process set forth in claim 5, wherein the initial pH of the bath is in the approximate range of 5.0 to 5.5.

7. The process set forth in claim 5, wherein the complexing and wetting agent is an alkylphenoxypoly(ethylcneoxy)ethanol having the following structure:

where R represents one or more alkyl substituents which possess from 5 to 18 carbon atoms and n is a number from 6 to 20 with an optimal value of 19.

8. The process set forth in claim 5, wherein the plating bath is utilized at a temperature in the approximate range of 7585C.

9. The process set forth in claim 5, wherein the direct current applied to the bath is in the approximate range of 0.060.09 amp/cm? 

1. The process of chemically plating a catalytic surface with nickel by treating the surface with an aqueous bath consisting essentially of a nickel salt, a hypophosphite, a complexing and wetting agent, a fluoride exaltant, a lead salt, succinates and lactates as exaltants, chelating agents and buffers, together with boric acid and ammonium hydroxide as buffers wherein the concentration of hypophosphite is approximately 0.1 to 0.3 mole/liter and the nickel ion concentration is approximately 0.2 to 0.3 mole/liter.
 2. The process set forth in claim 1, wherein the complexing and wetting agent is an alkylphenoxypoly(ethyleneoxy)ethanol having the following structure:
 3. The process set forth in claim 1, wherein the initial pH of the bath is in the approximate range of 5.0 to 5.5.
 4. The process set forth in claim 1, wherein the plating bath is utilized at a temperature in the approximate range of 75*-85*C.
 5. THE PROCESS OF CHEMICALLY PLATING A CATALYTIC SURFACE WITH NICKE BY TREATING THE SURFACE WITH AN AQUEOUS BATH CONSISTING ESSENTIALLY OF A NICKEL SALT, A HYPOPHOSPHITE, A COMPLEXING AND WETTING AGENT, A FLUORIDE EXALTANT, SUCCINATES AND LACTATES AS EXALTANTS, CHELATING AGENTS AND BUFFERS, TOGETHER WITH BORIC ACID AND AMMONIUM HYDROXIDE AS BUFFERS, WHEREIN THE CONCENTRATION OF HYPOPHOSPHITE IS IN THEAPPROXIMATE RANGE OF 0.1 TO 0.3 MOLE/LITER AND THE NICKEL ION CONCENTRATION IS IN THE APPROXIMATE RANGE OF 0.2 TO 0.3 MOLE/LITER, AND WHEREIN A SMALL DIRECT CURRENT IS APPLIED TO THE BATH WITH THE PLATING EQUIPMENT CONNECTED ANODIACALLY.
 6. The process set forth in claim 5, wherein the initial pH of the bath is in the approximate range of 5.0 to 5.5.
 7. The process set forth in claim 5, wherein the complexing and wetting agent is an alkylphenoxypoly(ethyleneoxy)ethanol having the following structure:
 8. The process set forth in claim 5, wherein the plating bath is utilized at a temperature in the approximate range of 75*-85*C.
 9. The process set forth in claim 5, wherein the direct current applied to the bath is in the approximate range of 0.06-0.09 amp/cm2. 